Fan



Nov. 14, 1933. H F, HAGEN 1,935,120

FAN

Filed Oct. 31, 1929 2 Sheets-Sheet l ZTraR/VEY Nov 14, 1933.

H. F. HAGEN FAN Filed Oct. 31, 1929 2 Sheets-Sheet 2 F/GZ /NVENTO/? M 1f Arm/ways Patented Nov. 14, 1933 UNITED STATES FAN Harold F. Hagen,Dedham, Mass., assignor to B. F. Sturtevant Company, Hyde Park, Mass., acorporation of Massachusetts Application October 31, 1929. Serial No.406,752

Claims.

The present invention relates to fans.

During periods of light load, mechanical draft fans are frequently shutdown to permit operation of the boilers on the stack draft alone. When I5 the fans are thus shut down, care must be exercised to make sure thatthe stack passages are unimpeded, otherwise severe damage-is likely toresult. output controlling devices, such as throttling means, in earlierconstructions, or spin controlling devices of the type described in myco-pending application Serial No. 210,666, filed August 4, 1927, anadditional burden is placed on the operator to open the passage duringperiods of stack l5 draft operation.

It is evident, however, that serious consequences may follow in theevent of neglect on the part of the operator.

The object of the present invention is to pro- ,20 vide automatic meansfor insuring an unimpeded draft passage for the flue gases whenever afan is shut down to permit operation on the stack draft alone.

With this object in view, the principal feature of the inventioncomprises by-pass means connecting the inlet and outlet of the fanadapted to be normally inoperative during operation of the fan butconstructed and arranged to open the passage upon shutting down of thefan. In

" its simplest form, the invention comprises a counter-balanced by-passdamper adapted to be actuated by the difference in pressure existingbetween the inlet and outlet of the fan upon the decrease in pressure inthe fan'outlet brought -85 about by operation of plant on the stackdraft.

Other features of the invention consist in certain novel features ofconstruction, combinations and arrangement of parts hereinafterdescribed and particularly defined in the claims. In the accompanyingdrawings, Fig. 1 is a side elevation of the preferred form of induceddraft fan and inlet and outlet connections embodying the features of thepresentinventidn; Fig. 2 is a front elevation .of the fan shown in Fig.1; and

Fig. S-is a fragmentary detail in section onan Inasmuch as fans areoften provided with During normal operation of the fan, the vanes areadjusted to any desired inclination to control the amount of flue gaseshandled by the fan. At the lightest load which the fan can handle at agiven speed, the vanes are entirely closed, the spin velocity being thena maximum and the gas being passed entirely through leakage spacesbetween the vanes. For even lighter loads, the fan is shut down and thestack draft is availed of to operate the plant.

Inasmuch as the stack draft alone is insufficient to create anyappreciable current of air through the vanes when closed, provision ismade for lay-passing the flue gases directly from the inlets to theoutlet. According to this construction, the plates 14 which are commonboth to the inlet scrolls and the outlet, are provided with bypassopenings 16. A swinging damper 18 is adapted normally to close eachopening. The

damper is adapted to swing inwardly as shown in Fig. 2, that is to say,into the outlet, upon a diminution of outlet pressure below the pressureexistingin the inlet.

Each damper normally closes against a flange 20 secured to the plate 14around-the opening. 30 The damper is provided with ears 22 which aresecured to a shaft 24 journaled in bearings 26 and 28. The bearing 26 isattached to the inner side of the plate 14 and the bearing 28 is mountedon, an angle iron 30 secured to the periphery 5 of the outlet box. v Theshaft is counter-weighted by means of an arm 32 carrying a ball 34. Thecounter-weight is nicely adjusted so that upon the slightest increase inpressure in the inlet over the outlet, the damper swings open. The 99damper is limited in its opening movement by a pair of stops 36 and 38secured to arcuate-brack- .ets 40 which are attached to the plate 14 at42.

, During normal operation of the fan, the pressure in the outlet issomewhat greater than the pressure in the inlet. The damper thereforeremains closed and in no way interferes with the mechanical draft. Thedamper remains closed for-all positions of the vanes 12 even when thelatter are in fully closed position, provided only 1 Bit are open whenthe fan is shut down. It is immaterial whether the vanes are opened ornot. If the vanes are opened, the difference in pressure between theinlet and outlet may not be sufllcient to open the damper but in suchcase, opening of the damper is unnecessary because a suflicientunimpeded passage is afforded through the fan itself. However, if thevanes are closed, the pressure diiference between the inlet and outletopens the damper and thus assures an unimpeded passage of air throughthe by-pass. The damper mechanism therefore operates automatically toavoid the consequence of careless operation.

It will be obvious that although the invention has been described asembodied in a construction employing spin controlling vanes for varyingthe output of the fan, such particular output controlling means is notessential, and the invention may be embodied in other constructionsemploying any type of output control such, for example, as throttlingmeans.

Having thus described the invention, what is claimed is:

1. A centrifugal fan having a rotor and a casing comprising an outletscroll and an inlet scroll at the side thereof with a partition between,the partition being provided with a by-pass opening, devices in theinlet scroll for controlling the flow of fluid from the inlet to therotor, and means normally closing the opening and opening automaticallywhen the flow of fluid through the rotor reaches apredetermined'minimum.

2. An induced draft fan adapted to receive fluid and deliver it to astack comprising a rotor, an outlet adapted to be connected to thestack, an inlet adapted to be connected to the source of the fluid,devices for controlling the delivery of fluid to the rotor, and normallyclosed by-pass me between the inlet and outlet operating automaticallyby the suction produced by the stack for opening said means when therotor is out of operation and said devices prevent the flow of fluidthrough the rotor.

3. The combination with a fan having an inlet, an outlet, a rotor, andoutput controlling means for varying the passage of fluid through therotor from inlet to outlet and having provision for substantiallyimpeding the passage of fluid when the rotor is stationary, of meansoperated automatically by a decrease of pressure in the outlet belowthat in the inlet to by-pass fluid around the output controlling means.

4. The combination with a fan having an inlet, an outlet, a rotor, andoutput controlling means for varying the passage of fluid through therotor from inlet to outlet and having provision for substantiallyimpeding the passage of fluid when the rotor is stationary, of by-passmeans around the output controlling means, and a pressure operateddamper in the by-pass means to open by a drop in pressure in the outletbelow that in the inlet, occasioned by stopping the rotor with saidoutput controlling means in closed position.

5. The combination with a mechanical draft fan having an inlet, anoutlet, and a rotor, and adapted to be connected to a stack to subjectthe outlet to a suction by stack draft, of output controlling means tovary the passage of air through the fan when .the rotor is running andadapted when closed to substantially impede passage of air with therotor stationary, and a by-pass damper normally closed and operated bythe stack suction to permit direct passage of air from the lid inlet tothe outlet on impeding the passage through the rotor.

F. HAGEN.

